Porous Hose Research Articles

A device for reducing wind and breaking flow into small-scale eddies to decrease infrasonic noise

The purpose of the fence developed is to raise the atmospheric boundary layer, and at the same time, break up the wind into small eddies, which interact destructively with one another and rapidly break down into smaller scales. This produces a calm region inside an enclosure or behind a wall with only random weak variations of the wind. Severe weather environments often have strong, complex regional flows. In the past, infrasonic systems have used spatial filters to average out the pressures from boundary layer turbulence. However, such spatial filters, while quite effective at lower wind speeds, do not reduce the wind noise sufficiently at higher wind speeds (e.g., above 10 m/s). This wind noise represented a critical limitation for infrasonic tornado detection systems. To solve this problem, we affixed the tops of barriers with corrugations. These cause the creation of adjacent vortex sheets of opposite signs, which interact strongly with one another and rapidly break down into smaller scales, and will not penetrate into regions behind the barrier. We use the eddy fence in conjunction with porous hose spatial filters. Although our motivation was to extend the effectiveness of infrasonic detectors in high wind conditions, there are numerous other applications.

Developments in infrasound sensors and wind noise reduction

As applications of infrasound grow so does the need for reasonably priced microphones and attendant wind noise reduction approaches. Many applications require sensor systems with frequency response between 0.01 and 10 Hz and a dynamic range between a few micropascals and ten Pascals and operate under severe environmental conditions. Sensor systems are often in remote areas with only occasional maintenance visits. Current installations usually employ classic condenser microphones or sliding wire microbarographs along with porous hose wind filters. Next generation sensors use optical fiber sensors long enough to average out wind noise or multiple sensors which allow for electronically canceling wind noise. Some of the advantages and characteristics of these sensors will be described. Calibration of sensors over the range of conditions remains a challenge. Progress on calibration facilities will be included in the discussion. [Work supported by the US Army Space and Missile Defense Command.]

Advances in distributed arrays for detection of infrasonic events

Infrasound arrays normally consist of four to eight microbarometers spaced kilometers apart. Each of these microbarometers is connected to a pipe or porous hose array to reduce wind noise. This presentation describes a 100 sensor all weather distributed array and its use in continuously logging infrasound signals over an extended period of time. The array has been deployed next to a conventional porous hose array connected to a Chaparral 2.5 microbarometer. The effectiveness of the two arrays in canceling wind noise and detecting infrasound signals is compared. The hardware and software used by the distributed array to log the data and to process it so as to cancel wind noise, identify and separate the infrasound signals, and locate their sources will be discussed.

An investigation of the correlation of infrasound signals as a function of sensor separation and wind velocity

Wind noise is a common obstacle to the detection and analysis of infrasonic signals. The masking caused by the wind noise is often reduced by spatial averaging via pipe or porous hose arrays. An alternate method is to average the signals from multiple sensors in distributed arrays. In order to reduce the wind noise, the sensors in the distributed array must be far enough apart so that their wind noise signals are incoherent, but not so far apart that the sound loses its coherence. Few measurements have been reported of the infrasound correlation distance in the presence of wind. This paper reports results of measurements of this infrasound correlation when the infrasound sensors are separated by distances up to hundreds of meters. Techniques for combining infrasound signals from widely separated sensors and measuring their correlation in the presence of wind noise are discussed.

An open-air infrasonic thermoacoustic engine

Wind noise at infrasound monitoring stations is a significant problem especially at the low frequencies of interest. Noise-reducing filters, typically consisting of radial arrays of porous hose, effectively area average the infrasonic pressure wave over a large space. The resulting area-averaged sound wave is then measured by a microbarometer. However, the only method to calibrate both the microbarometer and wind-noise filter is to use atmospheric or land-based man-made explosion. Thus, an infrasound source is needed that can calibrate both the microbarometer and the wind-noise filters in a safe way. A lowfrequency open-air thermoacoustic prime mover in a Helmholtz resonator has been constructed to fulfill this purpose. The system resonates at 10 Hz, is portable, compact, and safe to operate. The engine’s experimental and theoretical performance will be presented. [Work supported by a subcontract with the National Center for Physical Acoustics and a grant from the University Research Council at the University of Central Arkansas.]

Heterofazowe termoplastyczne kompozycje polimerowe modyfikowane odpadami gumowymi

The results of own research concerning new polymeric compositions based fully on secondary materials, obtained by physical modification, were presented. Recycled thermoplastics - PE-LD or PVC (Table 1) - were used as polymer matrix. Ground vulcanized rubber wastes of tires as well as thermally modified phosphogypsum (Table 2 and 3) or activated chalk were used as the fillers. Mechanical properties of such compositions (Table 4 and 5) and possibilities of their practical applications, with utilization of specific properties coming from the materials used, were discussed. It has been found that porous hoses made of such compositions show the properties qualifying them for use in the irrigation systems (Fig. 6). The compositions discussed can be also used as the fillers of noise damping screens (Fig. 7), fillers of columns for biological waste-water purification (Fig. 8) as well as for producing of the traffic safety devices or floorings.

Effect of atmospheric pressure fluctuations on low frequency and infrasound detection

A fundamental difficulty in low‐frequency and infrasound detection is the so‐called ‘‘wind noise’’ problem. At higher (>50 Hz), this wind noise is usually associated with the obstruction formed by the pressure pobe body. In this case, most of this wind noise can be adequately removed by the use of an appropriate wind screen. At lower frequencies ( 30 elements) 3‐axis pressure sensor array is used to quantify the relative magnitude of the intrinsic and induced pressure fluctuations. Signal processing algorithms are discussed which enchance the signal‐to‐noise ratio over that obtained using standard beam forming algorithms, by utilizing the localized nature of many of the fluctuations across the array. The effect of the height of the sensor above ground on the magnitude of the observed pressure flucutations is also examined using a 3‐axis linear pressure sensor array. Finally, the performance of a single‐element porous hose array is compared to that of a large‐element array.

The Sounds of Waves and Meteors

GEOPHYSICS The seismology division of the Royal Netherlands Meteorological Institute operates an array of micro-barometers that detects low-frequency (0.002 to 40 hertz) sound waves traveling through the atmosphere. This frequency range covers infrasonic disturbances inaudible to humans, such as distant nuclear explosions, and similar arrays are being installed worldwide as part of the Comprehensive Nuclear Test Ban Treaty. The Deelen array covers about 1.5 square kilometers and incorporates five porous hoses attached to each micro-barometer to reduce noise from atmospheric wind. Evers and Haak report detection on 8 November 1999 of a discrete 0.15 Hz component along with a continuous 0.19 Hz component. The 0.15 Hz signal came from the northeast, and the source was identified as a meteor explosion in the atmosphere over northern Germany, as confirmed by eyewitness accounts and photographs. The higher frequency signal came from the northwest (the northern Atlantic) and was associated with standing ocean waves coupled to the atmosphere (these sounds are called microbaroms). The authors estimated that the meteor explosion occurred at about 15 km in altitude and released energy equivalent to about 1.5 kilotons of TNT, within the range for nuclear explosions. — LR Geophys. Res. Lett. 28 , 41 (2001).

Infrasound detector design for recording sonic booms and events of CTBT interest

The Royal Netherlands Meteorological Institute (KNMI) is involved in a project concerning the detection of nuclear explosions and sonic booms. The main area of research and development is concerned with the infrasonic instruments. This includes the pressure sensor, electronics, and the noise-reducers. An optimal array-layout is necessary, next to a suitable instrument, to succesfully record infrasonic events. Therefore, the theoretical design of the array and practical implementation at Deelen are of main concern for the acquisitional part of the project. Once data are recorded, the data processing and interpretation has to be done. An on-line data analyses tool was developed to distinguish an infrasonic event from noise and other useless signals. The instruments are based on the Validyne Differential Pressure devices. To create an instrument sensitive in the 0.01–100 Hz frequency range, several constructional efforts were made p.e. acoustic capillary, backing volume, and signal inlet volume. The signal inlet volume is coupled to a noise-reducer, porous hoses or pipes. The symmetrical layout of the hoses/pipes guarantees an improvement in signal-to-noise ratio through spatial integration. The array of 16 microbarographs has an apeture of 2 km. Array techniques, i.e., slowness analyses, were applied to determine the most optimal layout.

Widespread Oxygen Bubbles To Improve Reservoir Releases

ABSTRACT This paper describes the installation and testing of an oxygen diffuser system in the forebay of TVA's Douglas Dam. The diffuser system is made up of plastic pipe frames and porous hoses that spread very small oxygen bubbles over a large area near the bottom of die reservoir. Operation of the system has demonstrated very high oxygen transfer efficiencies and a capacity to increase die hydropower discharge by 3 mg L−1 of dissolved oxygen.

A mathematical model of steady-state cross-flow microfiltration in a woven hose support

Cross-flow microfiltration is a technique in which the continuous build-up of filter cake is a avoided by pumping a slurry through a porous hose or tube. The filtrate permeats through the walls of the hose and the cake which develops on the inside of the walls is a continously scoured away by the slurry Presented in this paper is a four parameter mathematical model of cross-flow microfiltration which enables the effects of slurry concentration, pressure, slurry flow-rate and hose diameter on the steady-state flux of the filter to be quantified. The model has been verified for cross- flow microfiltration of calcium carbonate in a 25 mm diameter fabric hose.

The unsteady-state modelling of cross-flow microfiltration

Cross-flow microfiltration is a filtration technique in which the continuous build-up filter cake is avoided by pumping a slurry through a porous hose or tube. The filtrate permeates through the walls of the hose and the cake which develops on the inside of the walls is continuously scoured away by the slurry. In a previously presented work, a four parameter mathematical model of the cross-flow microfiltration was described. This enabled the effects of slurry concentration, pressure, slurry flow rate and tube diameter in the steady-state flux of the filter to be quantified. In this paper the transient behaviour of a cross-flow microfiltration system is examined. Two separate mechanisms are needed to explain the way filtrate flux changes with time : a relatively rapid change due to the change in the cake thickness and a gradual flux decline due to decreasing cake permeability.

A Method of Rapidly Applying Liquid Soil Insecticides1

Economical application of large quantities of dilute soil insecticides by means of a porous hose, the dilution of the active ingredient being effected by pumping into the water supply. Other applications for the method are suggested.